Solar energy collection utilizing heliostats

ABSTRACT

Heliostats are utilized to direct solar energy to a target configured for collecting the solar energy. The heliostats include mirrors that are adjustable so as to track the position of the sun relative to the target as the position changes over time. The heliostats are configured for self-alignment without the need for external control or surveying.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/680,375, filed Aug. 7, 2012, titled “METHOD TO POINT HELIOSTATS FOR SOLAR THERMAL POWER GENERATION” the content of which is both incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention relates generally to the collection of solar energy, in particular with the use of heliostats.

BACKGROUND

The design of a power generating plant based on solar energy may include a solar thermal collection tower surrounded by multiple heliostats. Each heliostat includes a mirror positioned to reflect solar energy from the sun to a collection target provided by the tower. Heat from the concentrated solar energy collected by the tower may be utilized to generate power, such as by producing steam that is then fed to a turbine to generate rotational energy, which in turn may be converted to electrical energy, or by employing solar cells to convert the solar energy directly to electrical energy.

For this type of system to collect solar energy efficiently, each heliostat needs to be able to track the sun accurately as the position of the sun changes during daylight hours, thereby ensuring that each heliostat reflects the sunlight onto the collection target. Because a significant number of heliostats may be employed at the plant (e.g., several thousands), relatively small inaccuracies in tracking (resulting in misalignment with the collection target) cumulatively may result in significant collection inefficiency and thus a large loss in the power generating capacity of the plant. Conventionally, successful tracking has required surveying the position and orientation of the heliostats relative to the spin axis of the earth, and predictions of the how the position of the sun relative to each heliostat changes over time, which may entail the consideration of several parameters such as date, time, and the longitude, latitude and elevation of each heliostat. In turn, conventional tracking has required that the heliostat be configured for precise mechanical adjustments of its mirror, and that the heliostat be capable of communication with the tower or other external device, adding to the cost of the system.

Therefore, there is an ongoing need for improvements in the field of solar energy collection, including heliostat-based sun-tracking techniques.

SUMMARY

To address the foregoing problems, in whole or in part, and/or other problems that may have been observed by persons skilled in the art, the present disclosure provides methods, processes, systems, apparatus, instruments, and/or devices, as described by way of example in implementations set forth below.

According to one embodiment, a method for collecting solar energy includes: positioning a minor of a heliostat such that the minor receives solar energy along a direction of incidence and directs solar energy to a target along a direction of reflection; and maintaining the minor in alignment with the target by: operating an image capturing device of the heliostat to capture an image of the sun and an image of the target; determining a centroid of the image of the sun and a centroid of the target; averaging the centroids to obtain an averaged centroid, wherein the averaged centroid is located at a distance from a reference pixel (corresponding to the minor surface normal) on the image capturing device; and adjusting the mirror to an aligned position at which the distance between the averaged centroid and the reference pixel is about zero.

According to another embodiment, a heliostat includes: a mirror movable along or about one or more axes; an adjustment device configured for moving the mirror; an image capturing device positioned for capturing an image of the sun and an image of a target; and a controller in signal communication with the image capturing device and with the adjustment device, the controller configured for: receiving signals from the image capturing device corresponding to the image of the sun and the image of the target; determining a centroid of the image of the sun and a centroid of the target; averaging the centroids to obtain an averaged centroid, wherein the averaged centroid is located at a distance from a reference pixel on the image capturing device; and controlling the adjustment device to adjust the minor to a position in alignment with the target, at which position the distance between the averaged centroid and the reference pixel is about zero.

According to another embodiment, a solar energy collection system includes: a target configured for collecting solar energy; and a plurality of heliostats arranged such that each heliostat is capable of being aligned with the target along a respective direction of reflection.

Other devices, apparatus, systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood by referring to the following figures. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the figures, like reference numerals designate corresponding parts throughout the different views.

FIG. 1 is a schematic cross-sectional view of an example of a solar energy collection system according to some embodiments.

FIG. 2 is a schematic view of an example of a heliostat according to some embodiments.

FIG. 3 is a perspective view of an image capturing device of the heliostat.

FIG. 4A is a schematic illustration of a pixel array of an image capturing device of a heliostat, when a mirror is properly aligned with a target.

FIG. 4B is a schematic illustration of the pixel array when the minor is misaligned with the target.

FIG. 5 is a schematic view of an upper portion of a solar thermal collector tower according to some embodiments.

DETAILED DESCRIPTION

FIG. 1 is a schematic cross-sectional view of an example of a solar energy collection system 100 according to some embodiments. The solar energy collection system 100 generally includes one or more targets 104 surrounded by a plurality of heliostats 108, which collectively may be referred to as a heliostat field. Generally, the target 104 may be (or be part of) any device configured for collecting (receiving) solar energy from one or more of the heliostats 108 such that the collected solar energy may be utilized for any appropriate purpose. In the illustrated embodiment, the solar energy collection system 100 includes one or more solar thermal collector towers 112, each containing one or more targets 104. The solar thermal collector tower 112 and heliostats 108 are typically supported on an area of ground 116 (earth) in any suitable manner. The heliostats 108, while fixed in position during operation, are typically removable from their fixed positions so that they may be serviced or replaced as necessary. The ground 116 is schematically illustrated as being flat by example only. The terrain surrounding the solar thermal collector tower 112 may vary in elevation, such that different heliostats 108 may be positioned at different elevations. Moreover, the heliostats 108 need not be uniformly distributed throughout the entire area of the heliostat field, nor does each heliostat 108 need to be equally spaced from other heliostats 108 adjacent thereto. For example, the heliostat field may contain gaps or regions of appreciable size in which no heliostats 108 are present. For purposes of the present disclosure, generally no limitation is placed on the size of the heliostats 108 or solar thermal collector tower 112, or on the size of the area occupied by the heliostat field or the number of heliostats 108 included in the heliostat field. The number of heliostats 108 may be on the order of tens, hundreds, thousands, or millions.

The solar thermal collector tower 112 includes the target 104, a support structure or tower 120, and a solar collector 124 (or solar receiver) mounted at or near the top of the tower 120, typically at a higher elevation than the heliostats 108. The target 104 is, or is part of, the solar collector 124. The target 104 may be one or more focal points on the solar collector 124 optically aligned with one or more of the heliostats 108 during operation (assuming no alignment errors). For example, the target 104 may be one or more apertures or regions distributed about the main (e.g., vertical) axis of the solar collector 124. The target 104, or the target 104 and solar collector 124, may have any configuration suitable for receiving solar energy from one or more of the heliostats 108, and concentrating and/or transmitting the received solar energy to other components of the solar thermal collector tower 112 as needed for a particular implementation. The tower 120 may be a structure configured primarily for supporting the solar collector 124, or may additionally include one or more housings or enclosures containing components utilized for processing the solar energy received from the heliostats 108. For example, the heat associated with the collected solar energy may be concentrated and deposited in water, or in another type of heat transfer medium (e.g., liquid metal, molten salt, air, etc.) in thermal communication with water, to produce steam. The steam may be utilized to produce electricity in a known manner, such as by feeding the steam to a turbine and converting the as-generated rotational energy of the turbine into electrical energy. As another example, the collected solar energy may be directly converted into electrical energy in a known manner by means of photovoltaic or thermoelectric devices. More generally, for purposes of the present disclosure, the solar thermal collector tower 112 may include a variety of components related to optics, energy conversion, heat exchange, fluid movement, power generation, and the like, all of which are understood by persons skilled in the art and thus need not be described in further detail herein.

Each heliostat 108 includes a movable (adjustable) minor 128 supported by a structure or frame, which may be a housing 132 that encloses various components. The minor 128 may be composed of any material suitable for efficiently reflecting solar photons over a desired (typically broad) range of wavelengths, which may include ultraviolet (UV), visible (Vis), and infrared (IR) wavelengths. This reflectivity may be a bulk property of the minor 128, or a property of a coating or film or layer applied to a substrate of the minor 128. As one class of examples, the minor may be a polished metal known to be highly reflective of sunlight, such as aluminum. Generally, no limitation is placed on the size (area) of the minor 128. Larger minors may require a lesser total number of heliostats 108 in the field. The total area covered by the minors 128 in the heliostat field may be on the order of tens, hundreds, thousands, or millions of meters squared (m²). The mirror 128 is typically planar (flat) as shown in FIG. 1. Alternatively the minor may be curved, in which case the center point of the mirror lies in a plane occupied by the flat mirror 128 shown in FIG. 1 (i.e., the reference plane of a curved mirror).

As shown in FIG. 1, the minor 128 of each heliostat 108 receives incident solar energy from the sun 136 along a line or direction of incidence (incident solar energy 140) and reflects the incident solar energy along a line or direction of reflectance (reflected solar energy 142). To maximize the collection of reflected solar energy 142 by the solar thermal collector tower 112, the reflected solar energy 142 should be (optically) aligned with the target 104 associated with a particular heliostat 108. Otherwise, the solar energy 142 reflected from the heliostat 108 will not be directly incident on the target 104—a condition often termed “spillage.” FIG. 1 depicts a bisector 146 between the direction of incidence and the direction of reflectance. The bisector 146 splits the angle between the direction of incidence and the direction of reflectance into equal halves α(i) and α(r). When the bisector 146 is perpendicular to the mirror 128 (i.e., is perpendicular to a planar minor, or to the reference plane of a curved minor as defined above), the minor 128 is said to be optically aligned with the target 104. As described further below, each heliostat 108 is configured to independently track the position of the sun so as to maintain its minor 128 in optical alignment with the target 104 during daylight hours.

FIG. 2 is a schematic view of an example of the heliostat 108 according to some embodiments. The minor 128 of the heliostat 108 is movably supported on an adjustment device 150, which is in turn supported by the frame or housing 132. The adjustment device 150 is configured for adjusting (moving) the minor 128, along (translation) and/or about (rotation) one or more, and typically two or more, axes. In the illustrated embodiment, the adjustment device 150 is configured for adjustably rotating the mirror 128 about two axes. Thus, the adjustment device 150 may include a rod 152 that communicates with the minor 128 so as to rotate the mirror 128 about a first (e.g., vertical) axis, as indicated by an angle θ. To drive the rotation of the minor 128 about the first axis, the rod 152 may communicate with a suitable motor 154 through any suitable actuator and/or linkage. The adjustment device 150 may also include a pivoting device 156 that communicates with the mirror 128 so as to rotate the mirror 128 about a second axis (e.g., a horizontal axis), that may be orthogonal to the first axis, as indicated by an angle β. To drive the rotation of the minor 128 about the second axis, the pivoting device 156 communicates with a suitable motor 158 through any suitable actuator and/or linkage. The motors 154 and 158 may be of any suitable type such as, for example, stepper motors or servo motors. The methods disclosed herein allow adjustment of the minor 128 to be performed without requiring particularly high precision. Hence, motors suitable for the present embodiment may be relatively inexpensive and/or simple in design.

The motors 154 and 158 may be in signal communication (wired or wireless) with, and thus be controlled by, any suitable controller 162. In some embodiments, the controller 162 is integrated with the heliostat 108, for example the controller 162 may be contained in the housing 132. In typical embodiments, the controller 162 is an electronic processor-based controller, such as may be embodied in an integrated circuit (e.g., an application specific integrated circuit, or ASIC) or chip as understood by persons skilled in the art.

The heliostat 108 also includes an image capturing device 164 (or light sensor, or photosensor) for capturing images of the sun 136 and the target 104 (FIG. 1). As described further below, the image capturing device 164 is configured for producing electrical signals utilized to determine whether the mirror 128 is properly aligned with the target 104 and, if misaligned, what type of adjustment is needed to correct the alignment error. In some embodiments, the image capturing device 164 is a multi-pixel device configured for capturing light and converting the light into electrical signals for further processing. In some embodiments, the image capturing device 164 is or includes a pixel array such as a focal plane array (FPA). The FPA generally includes a planar, two-dimensional array (rows and columns) of light-sensitive pixels. The design and operation of the FPA may be based on any suitable, known technology, such as that of complementary metal oxide semiconductor (CMOS) based devices, charge-coupled device (CCD) cameras, planar Fourier capture array (PFCA) based devices, etc. The FPA may be in signal communication with a readout integrated circuit (ROIC). The ROIC may be integrated with or attached to the FPA, or may be part of the controller 162. In either case, the FPA or other type of image capturing device 164 is in signal communication with the controller 162 via a wired or wireless communication link. The methods disclosed herein do not require a particularly high level of sensitivity, resolution, or image processing capacity. Hence, the FPA or other type of image capturing device 164 may be (or may be derived from) a relatively inexpensive, widely available device such as, for example, a camera of the type commonly provided with cellular telephones (which are typically CMOS based). The image capturing device 164 may be mounted to the reflective surface of the mirror 128, and may be fixed in position by a suitable adhesive and/or fastening means. In the illustrated embodiment, the image capturing device 164 is mounted at an edge or corner of the mirror 128. Alternatively, the minor 128 may be mounted to a substrate or plate, and the image capturing device 164 may be mounted to the substrate or plate instead of being mounted directly to the reflective surface of the minor 128, in which case the image capturing device 164 is nonetheless mounted such that the orientation of the image capturing device 164 is maintained in registry with the orientation of the minor 128.

In some embodiments, the heliostat 108 may include a data line 168 for transmitting data between the heliostat 108 and an external communication network or computing device. In some embodiments, however, the controller 162 is configured for controlling all normal operations of the heliostat 108, including reading signals from the image capturing device 164 and, in response, controlling the motors 154 and 158 to adjust the position of the minor 128 as needed for sun-tracking purposes during the day. In such a case, the data line 168 may be optional or utilized for other purposes such as diagnostics or data logging.

In some embodiments, the heliostat 108 may include a power line 170 for supplying electrical power to the heliostat 108 from an external power source. In other embodiments, however, the heliostat 108 may be self-powered. For example, the heliostat 108 may include an electrical storage reservoir 172 (or electrical power supply) such as a battery that supplies power to the controller 162, motors 154 and 158, and any other power consuming component of the heliostat 108 through power distributing circuitry 174. Such a battery may be replaceable or rechargeable. As a further example, the heliostat 108 may include a photovoltaic device 176 (i.e., solar cell(s)) positioned such that the sun 136 is in the field of view (FOV) of the photovoltaic device 176 for a sufficient amount of time during the day to charge the electrical storage reservoir 172.

FIG. 3 is a perspective view of the image capturing device 164. In this embodiment, the image capturing device 164 includes a fisheye lens 380 mounted to the minor 128 (a section of which is shown in FIG. 3). The fisheye lens 380 focuses images of the sun 136 and target 104 onto respective pixels of the image capturing device 164, which generally may be located in the focal plane of the fisheye lens 380. The fisheye lens 380 provides a wide FOV, for example about 170 degrees.

An example of operating the heliostat 108 will now be described with reference additionally being given to FIGS. 4A and 4B. FIG. 4A is a schematic illustration of a pixel array (e.g., FPA) 482 of the image capturing device 164 when the minor 128 is properly aligned with the target 104. The pixel array 482 is defined by a number of rows and columns of individual pixels 484. The number of rows and columns, and the number of pixels 484 in each row and column, are arbitrarily represented by example in FIGS. 4A and 4B. A reference pixel, which may be the center pixel, is marked by an “X”. At any given time during operation (daylight hours), the pixel array 482 captures images of the sun 136 and the target 104, and the controller determines the respective centroids 486 and 488 of these two images, which may be considered as x-y coordinate positions on the pixel array 482. The controller 162 then averages the two centroids 486 and 488 to obtain an averaged centroid, and determines the distance between the averaged centroid and the reference pixel. In FIG. 4A, the centroid 486 of the image of the sun 136 and the centroid 488 of the image of the target 104 are located at equal distances from the reference pixel. This position of the mirror 128 corresponds to the desired alignment of the mirror 128 with the target 104, which results in the reflected solar energy 142 being pointed directly at the target 104 (see FIG. 1). At this position, the solar energy 142 reflected by the mirror 128 of this particular heliostat 108 is efficiently collected by the target 104 with no spillage. In this case, the coordinate position of the averaged centroid corresponds to the position of the reference pixel, i.e., the distance between the averaged centroid and the reference pixel is zero, indicating that the minor 128 is properly aligned with the target 104 at that given time.

By comparison, FIG. 4B is a schematic illustration of the pixel array 482 when the minor 128 is misaligned with the target 104. In this case, an averaged centroid 490 of the centroid 486 of the sun's image and centroid 488 of the target's image is shown to be located at a non-zero distance from the reference pixel. This non-zero distance may be considered to be an alignment error E of the mirror 128. The controller 162 is configured for determining what adjustments (movements) are required to bring the minor 128 back into alignment with the target 104—i.e., the axis or axes along or about which the mirror 128 is to be moved, and the direction and magnitude of the movement (rotation and/or translation) along or about the axis or axes. The controller 162 then sends appropriate control signals to one or both motors 154 and 158 (FIG. 2) as needed to correct the alignment error. Alignment is corrected when the error E is driven back to about zero, which in the present context means a range of values that includes zero plus/minus an acceptable tolerance. Accordingly, correcting the error E entails eliminating the error E or at least minimizing the error E. It will be noted that although the fisheye lens 380 (FIG. 3) produces distortions and its mapping function is nonlinear, the distortions are symmetrical around the reference pixel X, thus allowing the error E to be corrected in the manner just described.

It will also be noted that the intensity of the images of the sun 136 and target 104 may be far greater than the intensity of other types of images that may possibly be within the FOV of the image capturing devices 164, such as clouds, trees, buildings, etc., in which case such other images are not likely to impair accurate calculation of the centroids 486 and 488. In some embodiments, however, the controller 162 may be configured to discard such other images upon capture. For example, the controller 162 may be configured to eliminate or zero-out any image having an intensity below a certain threshold value. This may, for example, be done in a binary manner in which the intensity values for the images of the sun 136 and target 104 are normalized to “1” and the intensity values for all other images captured are set to “0”.

The controller 162 may be programmed to check for alignment and make corrections as described above any number of desired times during operation (daylight hours) to track the sun with a desired degree of accuracy. The heliostat 108 may also be configured to allow a user of the heliostat 108 to make on-demand or spot checks by sending a command to the controller 162 by any means. For example, such a command may be sent remotely via a data line 168 (FIG. 2), by optical communication with the image capturing device 164 (described below), or by other means of communication.

In some embodiments, the solar energy collection system 100 includes one or more light sources (e.g., lamps). The light sources are positioned, or are movable into positions, such that each light source is in optical communication with (is able to transmit light to) one or more corresponding heliostats 108. In some embodiments one or more of the light sources may be mounted to the solar thermal collector tower, as illustrated in FIG. 5. Specifically, FIG. 5 is a schematic view of an upper portion of a solar thermal collector tower 512 that includes a solar collector 520 mounted on a tower 516, providing a target as described above. In this embodiment, the solar thermal collector tower 512 also includes one or more light sources 502 positioned at intervals around the axis of the solar thermal collector tower 512. Each light source 502 is mounted on an arm 506 that is movably mounted to the solar thermal collector tower 512. By this configuration, each light source 502 is selectively movable into a position between the target and one or more heliostats 108. In the illustrated embodiment, each light source 502 is rotatable with the corresponding arm 506 about a pivot axis 510. Accordingly, each light source 502 is movable into the line of sight of one or more image capturing devices 164 (FIG. 2), and when not in use is movable out of the line of sight (e.g., rotated downward and out of the way of the target). That is, each light source 502 is movable between an operating position and a non-operating position. As appreciated by persons skilled in the art, movement of the light sources 502 may be motorized and may be automated (and scheduled) by any suitable electronics-based control device that is either integrated with or remote from the solar thermal collector tower 512.

Each light source 502 may be utilized to establish a one-way optical communication link with one or more image capturing devices 164 (FIG. 2) of one or more respective heliostats 108. The light emitted from the light source 502 may be utilized to encode commands received by the image capturing device 164 and interpreted by the controller 162 of the heliostat 108. For example, a code may be based on a set of defined pulse sequences, with different commands being distinguished by different pulse sequences. The pulse sequences may be implemented by flashing the light source 502. A given pulse sequence may be constructed by a unique combination of pulse parameters, such as total number of pulses over a defined period of time, duration of each pulse, and time interval between pulses. One or more pulses of a given pulse sequence may have different durations than other pulses of the same pulse sequence. Likewise, the time intervals between adjacent pulses of a given pulse sequence may be different than the time intervals between other adjacent pulses of the same pulse sequence.

A command may be prefaced by a header (i.e., a beginning portion of a pulse sequence) that identifies an individual heliostat 108 and distinguishes that heliostat 108 from other heliostats 108. Headers may be correlated with the serial numbers or other unique indicia of respective heliostats 108 operating in the field. Indicia may, for example, be embodied in a bar code or RFID tag. Upon initial installation in the field, the indicia of each heliostat 108 may be correlated with its position (e.g., GPS coordinates), and a database may be maintained that provides a record of each heliostat 108 and its position in the field. In a case where a given light source 502 is positioned in the line of sight of multiple heliostats 108, prefacing a command with a header enables the command to be given to a selected one of the heliostats 108 only. The controller 162 of each heliostat 108 may be configured to respond to a command only if the controller 162 reads the header associated with that particular heliostat 108, and otherwise to ignore the command.

Optical communication with the heliostats 108 may be done for a variety of purposes. For example, all heliostats 108 in the field, or one or more selected heliostats 108, may be interrogated to determine whether they are working properly. Such diagnostics may be performed during nighttime, for example on each day starting at midnight, so as not to interfere with normal daylight operation. Nighttime diagnostics may be initiated by moving the light sources 502 to the operating positions described above and activating the light sources 502. Cameras—for example cameras 514 positioned near the light sources, cameras 518 positioned on the tower 520, or cameras positioned around the tower 520 in the heliostat field (not shown)—may be utilized to determine whether the light from one of the light sources 502 is being reflected from the respective mirrors 128 of the heliostats 108 being interrogated. Depending on the locations of the light sources 502, each heliostat 108 to be interrogated may first be commanded to move its minor 128 into alignment with a corresponding light source 502 (i.e., move the mirror 128 to a test position), for example by transmitting a light pulse sequence as described above. Images produced by the cameras may be evaluated to determine whether the heliostat field contains any location at which an expected mirror reflection of the light is absent. Then one or more heliostats 108 at and/or around that location may be tested to ascertain whether they are working properly or whether a component (e.g., image capturing device, motor, circuitry, mechanical linkage, wiring, etc.) has failed. For example, additional minor movement commands may be sent to suspect heliostats 108 and their responses observed. A minor jamming in the mechanics of a heliostat 108 may be self-fixable by commanding the heliostat 108 to move its mirror 128 back and forth along or about one or more directions.

As another example, the light sources 502 may be utilized to initialize the operation of the heliostats 108 each day. After sunset, the target 104 (or associated solar collector 124) is no longer a source of bright light. Yet, it is desirable to be able to begin the process of collecting solar energy as soon as the sun 136 rises and moves into the FOV of the heliostats 108. It is thus desirable at this time for the minors 128 of the heliostats 108 to be in at least an approximate alignment with the target 104 so that the heliostats 108 can begin to direct sunlight to the target 104. Methods disclosed herein may be performed to align the mirrors 128 by utilizing the light sources 502 as a substitute for the target 104 until the target 104 subsequently heats up. For example, a heliostat 108 may be operated to capture respective images of the sun 136 and one of the light sources 502, calculate the respective centroids of these two images, average the centroids, determine whether an alignment error exists, and adjust the minor 128 to minimize the alignment. Once the target 104 heats up to the point that it is able to serve as a sufficiently illuminated image to be captured by the image capturing devices 164 of the heliostats 108, the light sources 502 may be deactivated and moved out of the line of sight between the target 104 and the heliostats 108.

It will be understood that one or more of the processes, sub-processes, and process steps described herein may be performed by hardware, firmware, software, or a combination of two or more of the foregoing, on one or more electronic or digitally-controlled devices. The software may reside in a software memory (not shown) in a suitable electronic processing component or system such as, for example, the controller 162 schematically depicted in FIG. 2. The software memory may include an ordered listing of executable instructions for implementing logical functions (that is, “logic” that may be implemented in digital form such as digital circuitry or source code, or in analog form such as an analog source such as an analog electrical, sound, or video signal). The instructions may be executed within a processing module, which includes, for example, one or more microprocessors, general purpose processors, combinations of processors, digital signal processors (DSPs), or application specific integrated circuits (ASICs). Further, the schematic diagrams describe a logical division of functions having physical (hardware and/or software) implementations that are not limited by architecture or the physical layout of the functions. The examples of systems described herein may be implemented in a variety of configurations and operate as hardware/software components in a single hardware/software unit, or in separate hardware/software units.

The executable instructions may be implemented as a computer program product having instructions stored therein which, when executed by a processing module of an electronic system (e.g., the controller 162 in FIG. 2), direct the electronic system to carry out the instructions. The computer program product may be selectively embodied in any non-transitory computer-readable storage medium for use by or in connection with an instruction execution system, apparatus, or device, such as a electronic computer-based system, processor-containing system, or other system that may selectively fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this disclosure, a computer-readable storage medium is any non-transitory means that may store the program for use by or in connection with the instruction execution system, apparatus, or device. The non-transitory computer-readable storage medium may selectively be, for example, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device. A non-exhaustive list of more specific examples of non-transitory computer readable media include: an electrical connection having one or more wires (electronic); a portable computer diskette (magnetic); a random access memory (electronic); a read-only memory (electronic); an erasable programmable read only memory such as, for example, flash memory (electronic); a compact disc memory such as, for example, CD-ROM, CD-R, CD-RW (optical); and digital versatile disc memory, i.e., DVD (optical). Note that the non-transitory computer-readable storage medium may even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured via, for instance, optical scanning of the paper or other medium, then compiled, interpreted, or otherwise processed in a suitable manner if necessary, and then stored in a computer memory or machine memory.

It will also be understood that the term “in signal communication” as used herein means that two or more systems, devices, components, modules, or sub-modules are capable of communicating with each other via signals that travel over some type of signal path. The signals may be communication, power, data, or energy signals, which may communicate information, power, or energy from a first system, device, component, module, or sub-module to a second system, device, component, module, or sub-module along a signal path between the first and second system, device, component, module, or sub-module. The signal paths may include physical, electrical, magnetic, electromagnetic, electrochemical, optical, wired, or wireless connections. The signal paths may also include additional systems, devices, components, modules, or sub-modules between the first and second system, device, component, module, or sub-module.

More generally, terms such as “communicate” and “in . . . communication with” (for example, a first component “communicates with” or “is in communication with” a second component) are used herein to indicate a structural, functional, mechanical, electrical, signal, optical, magnetic, electromagnetic, ionic or fluidic relationship between two or more components or elements. As such, the fact that one component is said to communicate with a second component is not intended to exclude the possibility that additional components may be present between, and/or operatively associated or engaged with, the first and second components.

It will be understood that various aspects or details of the invention may be changed without departing from the scope of the invention. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation—the invention being defined by the claims. 

1. A method for collecting solar energy, the method comprising: positioning a minor of a heliostat such that the minor receives solar energy along a direction of incidence and directs solar energy to a target along a direction of reflection; and maintaining the mirror in alignment with the target by: operating an image capturing device of the heliostat to capture an image of the sun and an image of the target; determining a centroid of the image of the sun and a centroid of the target; averaging the centroids to obtain an averaged centroid, wherein the averaged centroid is located at a distance from a reference pixel on the image capturing device; and adjusting the minor to an aligned position at which the distance between the averaged centroid and the reference pixel is about zero.
 2. The method of claim 1, comprising repeating the steps of operating, determining, averaging, and adjusting one or more times.
 3. The method of claim 1, comprising operating a controller in signal communication with the image capturing device to receive signals corresponding to the captured images, determine the centroids, and average the centroids.
 4. The method of claim 3, comprising operating the controller to adjust the minor by sending a control signal to an adjustment device of the heliostat.
 5. The method of claim 4, wherein the adjustment device comprises a motor configured to move the mirror along or about an axis.
 6. The method of claim 3, wherein the controller is located at the heliostat.
 7. The method of claim 1, wherein the image capturing device is mounted on the minor.
 8. The method of claim 1, wherein the solar energy is transmitted through a fisheye lens enclosing the minor and the image capturing device.
 9. The method of claim 1, wherein the target is a solar thermal collector tower.
 10. The method of claim 1, comprising initializing operation of the heliostat by positioning a light source between the image capturing device and the target along the direction of reflection, and directing light from the light source to the image capturing device.
 11. The method of claim 10, comprising: capturing an image of the light source; determining a centroid of the image of the light source; averaging the centroid of the image of the sun and the image of the light source to obtain an averaged centroid, wherein the averaged centroid is located at a distance from a reference pixel on the image capturing device; and adjusting the minor to an aligned position at which the distance between the averaged centroid and the reference pixel is about zero.
 12. The method of claim 1, comprising sending a command to the heliostat by transmitting one or more light pulses to the image capturing device to produce a control signal, and operating a controller of the heliostat to read the control signal, wherein the command is encoded by the one or more light pulses.
 13. The method of claim 12, comprising operating the controller to move the mirror in response to the control signal.
 14. The method of claim 12, wherein transmitting comprises operating a light source between the image capturing device and the target.
 15. The method of claim 12, wherein transmitting is done during nighttime.
 16. The method of claim 12, comprising operating the controller to move the mirror to a test position in response to the control signal, wherein at the test position the mirror is aligned with a light source, and further comprising directing light from the light source to the minor, and determining whether the light is reflected in the mirror.
 17. The method of claim 16, wherein determining whether the light is reflected in the minor comprises operating a camera to capture an image of the mirror.
 18. A heliostat, comprising: a mirror movable along or about one or more axes; an adjustment device configured for moving the minor; an image capturing device positioned for capturing an image of the sun and an image of a target; and a controller in signal communication with the image capturing device and with the adjustment device, the controller configured for: receiving signals from the image capturing device corresponding to the image of the sun and the image of the target; determining a centroid of the image of the sun and a centroid of the target; averaging the centroids to obtain an averaged centroid, wherein the averaged centroid is located at a distance from a reference pixel on the image capturing device; and controlling the adjustment device to adjust the mirror to a position in alignment with the target, at which position the distance between the averaged centroid and the reference pixel is about zero.
 19. The heliostat of claim 18, wherein the adjustment device comprises a motor configured to move the mirror along or about an axis.
 20. The heliostat of claim 18, wherein the image capturing device is mounted on the mirror.
 21. The heliostat of claim 18, comprising a fisheye lens on the image capturing device.
 22. The heliostat of claim 18, comprising a photovoltaic array and battery for providing electrical power to one or more power-consuming components of the heliostat.
 23. A solar energy collection system, comprising: a target configured for collecting solar energy; and a plurality of heliostats according to claim 18, and arranged such that each heliostat is capable of being aligned with the target along a respective direction of reflection.
 24. The system of claim 23, wherein the target is a solar thermal collector tower.
 25. The system of claim 23, comprising a plurality of light sources, each light source movable between an operating position at which the light source is positioned in a line of sight of one or more of the image capturing devices of the heliostats and a non-operating position at which the light source is outside of the line of sight of the image capturing devices.
 26. The system of claim 25, wherein the light sources are mounted to the target.
 27. The system of claim 23, comprising a plurality of cameras, each camera positioned to capture an image of one or more of the mirrors of the heliostats.
 28. The system of claim 27, wherein the cameras are mounted to the target. 